The present invention relates to a combined service and parking brake, in particular for automotive vehicles.
A combined service a nd parking brake is disclosed in German patent application No. 37 32 303. The prior art brake has a hydraulic actuating device configured as a brake cylinder with two brake pistons which are movable in opposite directions. The brake cylinder is connected to the remaining brake system of a vehicle by way of a first hydraulic supply line. A second hydraulic supply line leads to a hydraulically operable locking device in the form of an auxiliary cylinder arranged at right angles relative to the brake cylinder. The auxiliary cylinder has an auxiliary piston adapted to slide a wedge between the two first-mentioned brake pistons in the brake cylinder in order to lock the two brake pistons in the applied condition. The disadvantage of the prior art arrangement is that two hydraulic supply lines are necessary for each brake. This increases the expenditure in material and assembly to a considerable extent.
Also, combined service and parking brakes are known in which a hydraulic actuating device is provided for service brake operations and mechanically operable locking devices are provided as parking brakes. However, the disadvantage of arrangements of this type is that an additional brake cable is required for each brake beside the hydraulic supply line. Further, this necessitates an increased expenditure in material and manufacture. In addition, the brake cable can only be fitted subsequent to mounting the brake on the vehicle. Normally, the assembly is not carried out by any competent brake manufacturer but is generally done by car makers. Apart from the shortcoming of an increased assembly effort, car makers additionally bear the risk of a wrong assembly.